This invention relates to projection screens for displaying an optical image, and more particularly to a projection screen formed of a matrix of optical unit cells.
The display of images on a projection screen is generally carried out under conditions of relatively low ambient light in comparison to the intensity of the light issuing from a projector.
If the surrounding light were relatively bright in comparison to the projected light, an insufficient lighting contrast condition might exist whereby the projected light would appear dull and indistinct, making it difficult for a viewer to perceive the images on the projection screen.
However, if the projected light can be focused at discrete locations on a projection screen, then the intensity of light provided by the projector can be maintained at a sufficient level to permit a distinctive display of images, even under conditions of relatively bright ambient light. To accomplish a desired focusing of light, I provide a projection screen formed of a matrix of optical unit cells that individually function as separate lenses which focus light onto discrete portions of the cell surface containing a light diffusing material.
The collective cell surfaces in the matrix cooperate to define the image display surface of the projection screen, such as shown in my U.S. Pat. No. 3,704,055. Each of the disclosed cells in this patent include a light converging lens spaced a predetermined distance from a concave reflecting mirror that reflects the light through a light diffusing material on the lens surface.
The focal point of the lens is selected to lie intermediate the lens surface and the reflecting mirror. A plane of opaque material surrounds the periphery of the concave reflecting mirror. Consequently, a compound surface must be formed, which includes a concave axial surface that is coated to provide the characteristics of a concave mirror, and a surrounding planar surface that is coated with opaque material.
It has been found that the equipment needed to produce the previously described optical cell is quite sophisticated and requires a high level of operator skill. Consequently, the manufacture of such an optical cell is not sufficiently cost effective to complete with other known projection screens that lack the advantages of the projection screen shown in my patent.
It is thus desirable to provide a projection screen formed of optical unit cells that is substantially more economical to produce than the known projection screen with optical unit cells. It is also desirable to provide a projection screen formed of optical unit cells that includes a reflection mirror having the same contour or surface characteristics as the surrounding surface with the opaque material, thereby eliminating the need to provide a compound surface for the mirror and the opaque material which surrounds the mirror.